1. Field of the Invention
The present invention relates to a multi-piece golf ball excellent in flight performance and shot feeling. More particularly it relates to a multi-piece golf ball having an improved shot feeling while retaining a low spin and high trajectory angle inherent in two-piece golf balls.
2. Description of the Prior Art
Hitherto, there have been used thread-wound golf balls and two-piece golf balls. The former is obtained by winding a rubber thread around a center filled with a solid or liquid and then covering the rubber-thread wound center with a cover mainly made of balata or synthetic resin. The latter is obtained by covering a rubber core with a cover made of a synthetic resin such as ionomer.
Thread-wound golf balls provides a good shot feeling because players receive small impact when hitting the ball and has a good controllability because players can impart intentional spin on the golf ball. However, since thread-wound golf balls are liable to spin, a sufficient flying distance cannot be secured in a wind ahead. In addition, they are poor in durability. As compared with thread-wound golf balls, two-piece golf balls have superior durability and can ensure a lower flying distance in a wind ahead because they are not susceptible to spin and have a relatively high coefficient of restitution. The high coefficient of restitution of the two-piece golf ball is resulting from the hard core, namely the core made from a hard material such as ionomor. However the hard core of the two-piece golf ball contributes to giving players a bigger impact than the thread-wound golf ball when hitting, which means inferior shot feeling to the thread-wound golf balls.
Japanese Patent Laid-Open Nos. 336617/1996, 336618/1996, 56848/1997, 248351/1997, 266959/1997 and 299510/1997 propose multi-piece golf balls which have improved shot feeling while ensuring a good flight performance of two-piece golf balls. The multi-piece golf balls have a multi-layered structure selected from the following groups: one has a core consisting of multi-layers; one has a cover consisting of multi-layers; and one has one or more intermediate layers placed between the cover and the core. And each layer constituting the multi-piece golf ball has an appropriate hardness to obtain both of a good flight performance and shot feeling.
The multi-piece golf balls as disclosed in the above publications are roughly classified into three groups: ones in which the outermost layer of a cover is the hardest and a relatively soft layer is placed on the inside of the cover (e.g., 336617/1996); ones in which a softer intermediate layer than the core encloses the core (e.g., 336618/1996); and ones in which an intermediate layer enclosing the core is the hardest of all layers constituting of the golf ball (e.g., 266959/1997, 248351/1997).
There are, however, demands on further improvements in shot feeling and flying distance. Because the shot feeling depends on clubs. For example, when a hard cover is employed in order to increase the coefficient of restitution, the resultant golf ball provides a poor shot feeling upon use of a putter, although it is possible to reduce impact when hitting golf ball by a driver or an iron, Accordingly, it is a primary object of the present invention to provide a golf ball which offers excellent shot feeling with any kind of club, while retaining a high coefficient of restitution inherent in solid golf balls.
According to the present invention, a multi-piece golf ball comprises an inner core which is positioned in a central part of the golf ball and has a JIS-C hardness of 75 or smaller; an outer core which encloses the inner core; an outer cover which is positioned in a surface part of the golf ball ; and an inner cover which is placed on the inside of the outer cover and has a JIS-C hardness of 80 or larger. A JIS-C hardness of the outer core is smaller than that of the other components, and a JIS-C hardness of the outer cover is larger than that of the other components.
A multi-piece golf ball of the present invention further comprises an intermediate layer between the outer core and the inner cover.